AN109 1Introduction of C Compiler

Introduction of C Compiler
How to Use Struct And Write Struct Data to
ROM Area
Below example 7 discribes how to store struct data in the
ROM and shows how to read struct data in the
function_read(). But the function_write(), which writes
data in the ROM area, is a bad example because
cook_data pointer indicates the ROM area. Example 8
describes struct copy function which copys struct data in
the ROM to struct variable in the RAM. It will be need in
the embedded system which has small RAM size. And
example 9 describes use of struct in the inline-asm.
When you use array of struct and a variable which indicate
a location of array, it will increase the ROM size
remarkablely. So, if you reduce a ROM size, you would
better change C to ASM like example 10. It will reduce a
ROM size dramatically. But if the locational variable of
array is a constant, ROM size of C is as same as one of
ASM.
typedef struct
{
unsigned char model;
unsigned char power_level[2];
unsigned char disp_data[2];
}cook;
cook RICE[] __attribute__ ((section(".text"))) = {
{1,100,100,4,5},
{2,100,100,3,4},
{3,100,100,2,3}
};
cook *cook_data;
cook data_ram;
unsigned char model, power, disp;
void function_read(void)
{
cook_data = &RICE[1];
model = cook_data->model;
power = cook_data->power_level[0];
disp = cook_data->disp_data[0];
}
// bad example
void function_write(void)
{
cook_data = &RICE[1];
cook_data->model = model;
cook_data->power_level[0] = power;
cook_data->disp_data = disp;
}
Example 7. Use of Struct
// struct size : 5bytes
void struct_copy(cook data_ram, cook cook_data)
{
unsigned char i;
for ( i=0 ; i